hey thats one sweet car - good work. I have a 320Si (black like your original) good fun on the road, and probably on the track, though I havent been brave enough to take it on one yet, (despite being an experienced racer for a number of years) as its my only road car and cant afford to bend it!
I understand what you say about the engine. On the road its ok though you have to keep the revs high to get into the zone. lots of grip and great handling.
Imagine it would appear to be a bit breathless round the ring against machines with easily more grunt. go for it and enjoy.